February 25, 2017

Homework Help: Physics(work and energy)

Posted by TOM on Sunday, May 20, 2012 at 12:50pm.

A cannon ball is fired so that it hits the wall at the top of a 10m tower.If the energy needed to destroy the wall is 49000 F and the mass of the cannon ball is 10 k, the minimum initial velocity of the cannon ball required to break the tower wall is

A 100 m/s
b 200 m/s
c 300 m/s
d 400 m/s

my way:
WD against friction + PEgain =KEloss
49000 + 10*10*10=1/2*(10)(u)^2 - 0

but is that way right?

who can told me the right one?

and if mine is correct,what is the principle behind?

why energy needed is equal to wd against friction?

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